Low alloy steel for sub-zero temperature application



LOW ALLOY STEEL FOR SUB ZERG of alloys whose heat treatment is notcritical. A more specific object is the provision of low alloy steelarticles:

having a mean value of toughness in excess of 15 foot pounds in theCharpy key hole impact tests at tempera- TEMPERATURE APPLICATION 5 turesas low as about -196 C. W The invention by means of which these objectsare igfigi $35,535, 33, gfigg figg g g 33:25:35; achieved is based onthe discovery that the addition of f New York small properlyproportioned quant1t1es of tantalum and optionally columbium tochromium-copper-nickel steels, N Drawillg-v App lily 1954, produces aremarkable lowering of the transition temsenal'No- 444,378 peratures ofsuch alloys. 5

This invention comprises alloys containing 0.02% to 8 Clams" (CL 75 124)0.15% carbon, 0.20% to 1.20% manganese, 0.05% to 0.60% silicon,0.20%--to 1.20% copper, 0.25% to 1.50% This invention relates to lowalloy steel for use at low chromium, 1.0% to 5.0% nickel, 0.03% to 0.30%temperature, and more particularly to alloys suitable aluminum, up to0.025% nitrogen and 0.05% to 0. for use in applications where superiorimpact resistance in the aggregate of tantalum and colum'bium, thetantaat sub-zero temperatures is requiredi lum content being at least0.04%, the remainder of. the- The trend of modern engineering practiceis toward alloys being iron, except for incidental impurities and. theutilization of extremely low temperatures for many 0 small quantities ofelements customarily found in steels and diverse operations. Steels withproperties which perof good quality. The preferred range of percentagesfor. mit their efficient use at sub-zero temperatures are needed-T thealloys of this invention is as follows: for chemical apparatus, piping,pressure vessels and for Percent facilities for the storage andtransportation of liquid gases. Carbon 0.02-0.10 The low temperaturefailures of steel articles usually 5 Manganese 0.20-0.60 result from lownotched bar impact strength, so that the Silicon 0.10-0.35 notchsensitivity of these materials is the critical factor in Copper 0.20-0.60 their selection. In general, materials having an impact" Chromium0.50-0.90 value of at least 15 foot pounds at a :given temperatureNickel 2.00-3.00 as determined by Charpy key hole. impact tests arelikely 0 Aluminum 005-020 to have adequate toughness for application ata similar Nitrogen 0.01-0.015 service temperature. Tantalum 0,05-0 1OSeveral alloys have been proposed for use at low temperatures, but theutility of each one of them has been Molybdenum may be present inquantities less than limited for. various reasons. Of these, au'steniticand high 0.01% up to 0.50%, and preferentially between 0.1% alloyferritic steels have the disadvantage of being. quite to 0.2%, if thicksections of the alloys are desired, incostly, of being difficult tofabricate, and of requiring asmuch as the thickness of the material isknown to be critical heat treating conditions for optimum properties. acritical factor in lowering the impact strength of such Economical lowalloy steels do not retain their toughalloys, which eflect thisadditional element will counteract. ness to sufiiciently lowtemperatures. In the case of these 40 The melting of the alloys of theinvention does not re a-lloys, variation in the heat treatment, becauseof its quire special. equipment or procedure, but conformstocriticality, will alter its properties, thereby rendering diflinormalpractice, such as, for. example, open hearth, arc cult thereproducibility of the desired properties of the furnace or melting inan induction furnace. The. heats steel. Hitherto, austenitic stainlesssteel has been the thus produced can then be but worked and normalized.most efficient'steel for low temperature service, but its and furthertreated by tempering at various temperawide applicability has beenlimited by economic factors. tures if desired.

TABLE I Charpy keyhole impact test (ft-lb.) alt-183 and 196 C.

Normalized 900 0. Normalized Percent Percent 900 C.

a Cb Temp. 600 O.- Temp. 600 C. Temp. 500 O. Temp. 550 O.- Temp. 650 C;-Added Added 1 Hour 5 Hours 1 Hour 1 Hour 1 Hour 183C 196C. 183 C. 196C183C. 196 C. 183C. C. 183C 196C 183C 196C 0.10 39.5 2%N1 k@1 8:33 W915?it? '"ifif 0.10 0 10 41.0 30.0 0.10 22.5 23.0 0.05 0.05 36.5 20.8 0.050. 05 28.0 23.5 3% Nickel 0.10 0.03 22.3 23.0 0.10 0.03 34.3 33.3 0.2520.0 0.20 0.05 39.5 32.5

It is the principal object of this invention, therefore, to provide arelatively inexpensive low allow ferritic steel Referring to theattached table of impact test results, Table I, samples of similarcomposition were heat treatsuitable for use in applications where verylow tempera- 7 0 ed in several ways to indicate thatheat treatment is.not

tures are normally encountered, and which will have. low transitiontemperatures. Another object is the provision critical, and that high.impact values are readily reproducible over a large number of heats inboth normalized Patented June 25, 1957- T which are well-suited for usein the fabrication'of articles U i and stress-relieved conditions. Thetypical nominal composition of each steel sample was:

A further indication of the effects produced by tantalum addition inlowering the transition temperature of low alloy chromium-copper-nickelsteels is indicated by the data of Table II. The composition of thesamples which do not contain tantalum is similar in everyother that arerequired to withstand severemechanical stress Percent Carbon 0.03

Manganese 0.30 Silicon 0.20

Chromium 0.80

Copper 0.50

Aluminum 0.15

Nitrogen l 0.013

respect to that of the chromium-copper-nickcl steels containing 3%nickel given on Table I; the impact tests rep sults' represent anaverage of seven tests from four heats at a --183 C. The notch toughnessfigures for the tantalum-bearing samples are representative of to 24tests from a total of 12 heats. In nearly all cases the mean value oftough-.

ness under various heat treatments exceedstheminimnm In addition to thehigher impact values obtained by the tantalum-containing alloys, thedata in Table II also demonstrate that the alloys which do not containtantalum are substantially affected by the difference in heat treatment,whereas proportionately similar results are obtained by the alloy ofthis invention under the different treatments.

The normalizing treatment as practiced in the present invention consistsof heating the steel to above the critical temperature but not so highas to produce material grain growth and subsequently cooling at arelatively rapid rate or in some cases, in a liquid coolant. The steelis cooled substantially to room temperature prior to heating fortempering. The exact mechanism whereby the tantalum addition lowers thetransition temperature of these alloys is not known, but it is believedthat this element produces a grain refinement by forming finelydispersed carbides within the grain structure and by retarding carbidesolution and reprecipitation during tempering of the low alloy steel.

Columbium can be effectively added in combination with tantalum up tosimilar percentages as long as the total of the two elements does notexceed 0.25%. While the composition as hitherto disclosed providesexcellent low temperature properties where the finished alloy bars donot exceed 1% inches in thickness, it has been found that the additionof 0.1% to 0.30% molybdenum in creases the toughness of the alloy inslower-cooling, heavier sections.

By the present invention cast or wrought steel articles are producedwhich may be hot worked and subsequently welded, normalized, ornormalized and tempered, and

at low temperatures Their toughness upon prolonged exposure to thesetemperatures recommends their employment where dependable operation isessential.

What is claimed is: 1. An alloy containing about 0.02% to 0.15% carbon;0.20% to 1.20% manganese; 0.05% to-0.60% silicon; 0.20% to 1.20% copper;0.25% to 1.50% chromiurn; 1% to 5% of nickel; 0.03% to 0.30%' aluminum;

up to 0.025% nitrogen and 0.05 to 0.25 in the aggregate of tantalum, andcolumbium, the tantalum content being at least 0.04%; up to 0.50% ofmolybdenum;

and the remainder iron and incidental impurities.

2. An alloy containingabout 0.02% to 0.15 carbon;

0.20% to 1.20% manganese; 0.05% to 0.60% silicon;

0.20% to 1.20% copper; 0.25% to 1.50% chromium; 1% to 5% of nickel;0.03% to 0.30% aluminum; up to 0.025% nitrogen; 0.01% to0.50%'molybdenurn and 0.05% to 0.25% in the aggregate of tantalum andcolurnbium, the tantalum content being at least 0.04%; the

remainder iron and incidental impurities. r

3. An alloy containing about 0.02% to 0.10%. carbon;

0.20% to 0.60% manganese; 0.10% to 0.35% silicon;

the tantalum content being at least 0.04%; the remainder iron andvincidental impurities.

' 5. 'A' welded article which in its normal use is required to withstandmechanical stress at low temperatures down I I 0.20% to 0.60% copper;0.50% to'0'.90% chromium; 2.00% to 3.00% nickel; 0.05% to 0.20%aluminum;

0.010% to 0.015% nitrogen; an aggregate of 0.05% to 0.10% of tantalumand columbium, thetantalum content being at least 0.04%; the remainderiron and incidental impurities.

4. An alloy containing about'0.'02%' to 0.10% carbon; 0.20% to 0.60%manganese; 0.10% to 0.35% silicon;

' 0.20% to 0.60% copper; 0.50% to .90% chromium; 2.00%

to 3.00% nickel; 0.05% to 0.20% aluminum; 0.010% to 0.015% nitrogen;0.10% to 0.20% molybdenum; an aggregate of 0.05 to 0.10% of tantalum andcolumbium,

to about -196 C., which article is composed of an alloy containing about0.02% to 0.15% carbon; 0.20% to 1.20% manganese; 0.05 to 0.60% silicon;0.20% to 1.20% copper; 0.25% to 1.50% chromium; 1.0% to 5% of nickel;0.03% to 0.30% aluminum; up to 0.025% nitrogen and 0.05% to 0.25% in theaggregate of tantalum and columbium, the tantalum content being at least0.04%; the remainder iron and incidental impurities.

6. A welded article which in its normal use is required to withstandmechanical stress at low temperatures down to about -196 C., whicharticle is composed of an alloy containing about 0.02% to 0.15% carbon;0.20% to 1.20% manganese; 0.05% to 0.60% silicon; 0.20% to 1.20% copper;0.25% to 1.50% chromium; 1.0% to 5% nickel; 0.03% to 0.30% aluminum; upto 0.025% nitrogen; 0.01% to 0.50% molybdenum and 0.05% to 0.25% in theaggregate of tantalum and columbium, the tantalum content being at least0.04%; the remainder iron and incidental impurities.

7. A welded article which in its normal use is required to withstandmechanical stress at low temperatures down to about 196 C., whicharticle is composed of an alloy containing about 0.02% to 0.10% carbon;0.20% to 0.60% manganese; 0.10% to 0.35% silicon; 0.20 to 0.60% copper;0.50% to 0.90% chromium; 2.00% to 3.00% nickel; 0.05% to 0.20% aluminum;0.010% to 0.015% nitrogen; an aggregate of 0.05% to 0.10% of tantalumand columbium, the tantalum content being at least 0.04%; the remainderiron and incidental impurities.

8. A welded article which in its normal use is required to withstandmechanical stress at low temperatures down to about 196 C., whicharticle is composed of an alloy containing about 0.02% to 0.10% carbon;0.20% to 0.60% manganese; 0.10% to 0.35% silicon; 0.20% to 2,797,162 50.60% copper; 0.50% to 0.90% chromium; 2.00% to 3.00% nickel; 0.05% to0.20% aluminum; 0.010% to 0.015% nitrogen; 0.10% to 0.20% molybdenum; anaggregate of 0.05% to 0.10% of columbium and tantalum, 1,373,908 thetantalum content being at least 0.04%; the remainder 5 2,103,610 ironand incidental impurities. 2,264,35 5

References Cited in the file of this patent UNITED STATES PATENTS PaczApr. 5, 1921 Macormac Dec. 28, 1937 Becket et a1. Dec. 2, 1941Offenhauer May 25, 1954

1. AN ALLOY CONTAINING ABOUT 0.02% TO 0.15% CARBON; 0.20% TO 1.20%MANGANESE; 0.05% TO 0.60* SILICON; 0.20% TO 1.20% COPPER: 0.25% TO 1.50%CHROMIUM; 1% TO 5% OF NICKEL; 0.03% TO 0.30% ALUMINIUM; UP TO 0.025%NITROGEN AND 0.05% TO 0.25% IN THE AGGREGATE OF TANTALUM AND COLUMBIUM,THE TANTALUM CONTENT BEING AT LEAST 0.04%; UP TO 0.50% OF MOLYBDENUM;AND THE REMAINDER IRON AND INCIDENTAL IMPURITIES.